The present invention relates to a chromium alloy and in particular to a chromium alloy for use at high temperatures, particularly for use as gas turbine engine components.
Currently gas turbine engine turbine blades and turbine vanes are manufactured from nickel based superalloys.
The use of chromium based alloys as alternative high temperature materials has also been suggested.
Chromium possesses a number of properties that are considered advantageous for high temperature applications. Chromium possesses a higher melting point than nickel, i.e. 1850° C. for chromium compared to 1450° C. for nickel, and exhibits reasonable oxidation resistance, lower density and lower cost than other elements that have similar or higher melting temperatures. However, chromium suffers from interstitial embrittlement, limited strength at high temperatures and deteriorating oxidation resistance above 1000° C.
U.S. Pat. No. 3,015,559 discloses a binary chromium alloy consisting of 0.5 to 6 wt % of a rare earth element selected from the group consisting of cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
U.S. Pat. No. 3,138,456 discloses a chromium alloy consisting of 0.5 to 7 wt % tantalum and 0.1 to 7 wt % of an element selected from the group consisting of titanium, vanadium, niobium, molybdenum, aluminium, silicon and mixtures thereof and the chromium content is not less than 85 wt %.
U.S. Pat. No. 3,841,847 discloses a chromium alloy consisting of at least 70 wt % chromium, up to 18 wt % yttrium, up to 18 wt % yttria, up to 5 wt % aluminium and up to 8 wt % silicon.
U.S. Pat. No. 6,245,164 discloses a chromium alloy consisting of up to 11 at % tantalum, up to 7 at % molybdenum and minor amounts of titanium, silicon, germanium, cerium, lanthanum, yttrium and other rare earth elements. This chromium alloy has a dual phase microstructure consisting of a Cr (Ta) solid solution and a Cr2Ta Laves phase. U.S. Pat. No. 6,245,164 states that hypoeutectic alloys which have a presence of tantalum in amounts not exceeding the eutectic composition show remarkable hardness and hypereutectic alloys which have the presence of tantalum above the eutectic composition become brittle and lose their impact resistance. U.S. Pat. No. 6,245,164 also states that the addition of silicon lowers the isothermal rate of oxidation but results in a greatly increased tendency to spall under thermal cycling conditions and at temperatures over 1000° C. the silicon reduces the oxidation resistance and causes spalling. U.S. Pat. No. 6,245,164 discloses that a specific chromium alloy consisting of 8.0 at % tantalum, 5.0 at % molybdenum, 3.0 at % silicon, 0.25 at % germanium, 0.2 at % lanthanum and the balance chromium has very good oxidation resistance at 1100° C.